Infer non-empty-list for preg_match_all() matches when the match succeeded

[phpstan-bot]

Summary

After a successful preg_match_all() (e.g. inside if (preg_match_all(...))), the resulting $matches arrays were inferred with plain list<...> value types. Because a list may be empty, accessing $matches[0][0] produced a false positive Offset 0 might not exist on list<string>.. A successful preg_match_all() returns the number of full matches, which is >= 1, so every produced list is guaranteed non-empty.

This change infers non-empty-list<...> for those lists when the match is known to have succeeded.

Changes

• src/Type/Php/RegexArrayShapeMatcher.php:
  • createSubjectValueType() now takes $wasMatched and intersects the PREG_PATTERN_ORDER subject list with NonEmptyArrayType when $wasMatched->yes().
  • createGroupValueType() intersects the PREG_PATTERN_ORDER per-group list with NonEmptyArrayType when $wasMatched->yes().
  • buildArrayType() intersects the PREG_SET_ORDER outer list with NonEmptyArrayType when $wasMatched->yes().
  • Updated the two non-matchesAll call sites of createSubjectValueType() to pass $wasMatched.
• tests/PHPStan/Analyser/nsrt/preg_match_all_shapes.php: updated existing matched-branch expectations to non-empty-list and added a bug14781() regression covering both PREG_PATTERN_ORDER and PREG_SET_ORDER, including safe $matches[0][0] access.

Root cause

RegexArrayShapeMatcher built the preg_match_all() result lists as ArrayType & AccessoryArrayListType without recording non-emptiness, even when the call was specified as a successful match ($wasMatched->yes()). The fix adds NonEmptyArrayType to the intersection at each of the three places that build a list for preg_match_all():

• PREG_PATTERN_ORDER subject list
• PREG_PATTERN_ORDER capturing-group lists
• PREG_SET_ORDER outer list

preg_match() (single match) and the non-matchesAll tagged-union branches were probed and are unaffected — they do not produce lists, so there is no non-emptiness to preserve. Non-constant patterns fall back to the generic param-out types and are likewise unaffected.

Test

• bug14781() in tests/PHPStan/Analyser/nsrt/preg_match_all_shapes.php asserts non-empty-list for both PREG_PATTERN_ORDER and PREG_SET_ORDER inside if (preg_match_all(...)), and that $matches[0][0] / $setMatches[0] no longer trigger possibly-missing-offset errors.
• Existing matched-branch assertions in the same file were updated from list to non-empty-list. Assertions outside a success check (plain calls, === 0 guards) correctly remain list.

Fixes phpstan/phpstan#14781